I didn't starch any of mine before doing it, if you washed it you may have to to stiffen it up some, most fabric have enough body to it without it, some prefer a little extra or washed it. it is up to you, what are you comfortable working with.
The stiffness helps when you are tryin to line up your repeats, of course then when starching it you have it a little off grain then you would have a time trying to line it up as well.